Among advisers to family-owned businesses there’s a widely known adage: “Shirtsleeves to shirtsleeves in three generations.” Difficult as it is to build a successful enterprise, it is more difficult to raise children with the ability and desire to keep it going. Producing one grandchild among a potentially rivalrous set of cousins with the right talent and interests and force and tact — is more challenging still.

Observers of Saudi Arabia have been mulling this problem for many years, as the strongest among founding king Abdul Aziz ibn Saud’s 45 sons passed the crown from one to another. Now, the murder of journalist Jamal Khashoggi, a Post contributing columnist lured to the Saudi Consulate in Turkey, chillingly tells us that generational succession is no longer a future problem. It is a present crisis.

Admittedly, thanks to the ocean of oil discovered beneath the sands of Saud’s realm, there’s no risk of his grandchildren reverting to the nomadic life from which the kingdom was built nearly a century ago. Instead, the risk is that the third generation — lacking its grandfather’s cunning and the caution of its fathers — will drag the kingdom into a spiral of treachery, backstabbing and recklessness. Crown Prince Mohammed bin Salman has shown himself to be steeped in all three.

MBS, as the crown prince is widely known, is the first of his very numerous generation (Saud had at least 22 wives) to wield the power of the crown; his father, King Salman, is 82 and partially disabled by Alzheimer’s disease. A young tyrant in a big hurry, MBS elbowed aside an older cousin last year, confining him to house arrest, and also set about jailing his rivals, torturing his critics, silencing dissenters, and creating a humanitarian crisis of staggering proportions in neighboring Yemen. Khashoggi’s murder, for all its alleged grisly sadism, seems right in character.

True, the House of Saud has never been known for liberalism. Oppressive at home and subversive abroad, it long ago made a devil’s bargain with radical Wahhabism that lies near the root of al-Qaeda, the Islamic State and the Taliban. Even so, dispatching a team of killers — allegedly packing a bone saw — to dispose of a prominent U.S. resident on Turkish soil is an act of alarming brashness.

I asked one knowledgeable business executive whether this tells us MBS is crazy or stupid. “Hmm,” came the answer. “Maybe both.”

Heedless leaders are bad enough in troubled byways such as Libya or Sudan. But to have one at the controls in Saudi Arabia is intolerable. This is arguably the United States’ strongest ally in the Muslim Middle East, and has been since President Franklin D. Roosevelt gave his blessing to Saud. The kingdom serves as a critical counterweight to Iran’s ambitions, and a reasonable custodian of the most sacred sites of Islam.

Set aside the oil — thanks to the fracking and efficiency revolutions, we don’t need it like we used to. The most precious resource the Saudis can offer today is stability in the heart of the world’s tinderbox.

Rather than stability, though, we get this impetuous crime, which no doubt unsettled old King Salman (who is not, I’m told, as enfeebled as some suggest) and his last surviving full brother, Prince Ahmed bin Abdulaziz. Though rivals, both men were raised in the cynical pragmatism of their generation of Saudi royals; surely they see that MBS has become bad for the family business.

Unfortunately, the crown prince still has friends in high places, having wormed his way into the naive hearts of the inexperienced Trump administration. After striking up a bromance with Jared Kushner — MBS flattered Kushner’s self-image as a Mideast peace broker — the budding strongman scored a Trump Tower audience with the newly elected president, Kushner and former Trump whisperer Stephen K. Bannon. Not an Arabist in the bunch.

Was the relationship greased by Saudi purchases of luxury Trump-branded properties? Special counsel Robert S. Mueller III is reported to be looking into that question. This much we know: From that gulling of the dupes came Trump’s first foreign travel: a lavish trip to Riyadh in May 2017, during which the crown prince blew so much smoke the president nearly floated home. The same Trump who trusts Russian President Vladimir Putin and loves Kim Jong Un of North Korea clambered aboard the MBS Express.

And, for a moment, all was lovely. The kingdom permitted movie theaters and allowed women to drive. MBS spoke of diversifying his economy and purging Islam of radicals.

Now we see what’s behind the facade.

Trump is not the first president to bet on the wrong foreign leader. But he should now use the United States’ considerable influence to steer the king toward a new succession plan. Khashoggi’s murder was a flagrant insult to the United States and to the president personally. To go groveling after its apparent author weakens Trump, weakens the United States, and makes Saudi Arabia a powder keg.

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David Von DrehleDavid Von Drehle writes a twice-weekly column for The Post. He was previously an editor-at-large for Time Magazine, and is the author of four books, including "Rise to Greatness: Abraham Lincoln and America’s Most Perilous Year" and "Triangle: The Fire That Changed America." Follow